Interaction of dipyridamole with phospholipid monolayers at the air-water interface: Surface pressure and grazing incidence X-ray diffraction studies

Incorporation of dipyridamole (DIP) in Langmuir monolayers of the zwitterio nic phospholipid dipalmitoylphosphatidylcholine (DPPC) has been investigate d using surface pressure isotherm and grazing incidence X-ray diffraction ( GIXD) measurements. An expansion in the pressure-area isotherms of the DPPC monolayer was observed, which was maximum in the liquid-expanded (LE) to l iquid-condensed (LC) transition region and at a DIP concentration of 2 mol% , Accordingly, the GIXD measurements indicated an expansion of the 2D latti ce in the LC phase up to a surface pressure of ca, 30 mN/m, A condensation effect on the DPPC packing for high DIP concentrations, as previously sugge sted, can be ruled out. (C) 2001 Elsevier Science B.V. All rights reserved.